When work is carried out using a lawn mower, normally, it is carried out with all of four wheels mounted on a cutter housing in contact with the ground. However, sometimes, to mount or dismount a place where there is a step, or to shake cut grass adhered to parts inside the cutter housing off onto the ground surface, a movement of lifting the front wheels about the rear wheels as a pivot is carried out. When this movement is carried out, an external force tending to bend the cutter housing in the length direction acts.
With respect to an external force of this kind, in a cutter housing made of resin, due to the rigidity and strength characteristics of the material, it is not possible to obtain adequate rigidity and strength.
In this connection, a lawn mower in which reinforcing ribs are formed in a resin cutter housing to provide the cutter housing with the necessary rigidity has been proposed, for example in JP-UM-B-4-40433.
This lawn mower of related art will now be described on the basis of FIG. 14 and FIG. 15 hereof.
The lawn mower 250 of related art shown in FIG. 14 has an engine 252 mounted on the top of a cutter housing 251. As shown in FIG. 15, a cutter blade 254 is attached to the output shaft 253 of the engine 252. A handle 255 (see FIG. 14) extends rearward from the cutter housing 251. Front wheels 256, 256 and rear wheels 257, 257 are attached to the cutter housing 251. The lawn mower 250 travels on these front wheels 256, 256 and rear wheels 257, 257 and cuts grass with the cutter blade 254. Flange parts 258, 258 are formed on the sides of the cutter housing 251. These flange parts 258, 258 have multiple reinforcing ribs 259, whereby the impact-resistance of the left and right side faces of the cutter housing 251 is increased.
However, in the lawn mower 250, because the multiple reinforcing ribs 259 are formed on the flange parts 258, 258, although they are strong with respect to impacts from the sides of the cutter housing 251, there has been the shortcoming that they make no contribution to the length-direction bending rigidity of the cutter housing 251. And it has also been the case that mud or cut grass enters between the reinforcing ribs 259, and this mud or cut grass has to be removed every time mowing work is carried out, so that the ease of maintenance of the lawn mower 250 is reduced.
Accordingly, a lawn mower has been awaited with which it is possible to increase the length-direction bending rigidity of the cutter housing and it is possible to increase the resistance to impacts from the sides of the cutter housing.